Camera systems using vehicle-mounted cameras in recent years include a function of displaying a guide line indicating an estimated location of a vehicle and superimposed on an image taken by a camera (hereinafter referred to as “camera image”) or a function of generating an image from a virtual viewpoint through geometric conversion of the camera image or the like. Both of these functions use association between a three-dimensional position in a real space and a two-dimensional position projected on the camera image. Implementing such association requires calculations (hereinafter referred to as “calibration,” as appropriate) of so-called camera parameters such as a setting angle or setting position of the camera or projective transformation parameters.
Calibration based on a camera image normally uses a calibration marker whose shape, size, and setting position or the like are known. As one such mode, there is a method that takes an image of a marker including a specific pattern set on a road surface and uses a projection position with respect to the camera image (e.g., see Patent Literature (hereinafter abbreviated as “PTL”) 1).
Moreover, as an example of a method using a marker having a polygonal shape, a method is known which takes an image of a square marker set on a road surface using a camera, projectively transforms the camera image, generates a bird's eye image and calculates a projective transformation parameter, which is an example of a camera parameter, based on the square shape and existing position in the bird's eye image (e.g., see PTL 2).